1. Field of the Invention
The present invention relates to a method for driving a plasma display panel in which any one of the sustaining electrode and scanning electrode is used commonly by the cells next to both sides thereof.
2. Description of the Related Art
Generally, plasma display panels are characterized in that they have a thin structure; almost no blinking or flickering occurs; they have a high display contrast; it is possible to have a relatively large screen area; they have a fast response speed; and they are of self-luminous type enabling emission of the multi-colored light by using fluorescent materials. Therefore, in recent years plasma display panels have been used extensively in the computer-related display device field, color-image display field, and the like.
According to the method of operation, the plasma display panels are classified into AC-type plasma display panels that are run in the alternating current discharge mode indirectly as the electrodes are coated with a dielectric substance and DC-type plasma display panels that are run in the direct current discharge type as the electrodes are exposed to the discharging space. The AC-type plasma display panels are further classified into those of memory-run type using the display cell memory and those of refresh-run type not using the display cell memory according to the method of driving. Also, brightness of the above refresh-run-type plasma display panels is lowered if the display capacity is increased. This is because brightness of plasma display panels is proportional to the frequency of discharge. For that reason, the memory-run-type plasma display panels are used mainly when running the highly bright and large-capacity display.
FIG. 1 is a perspective diagram of the relevant parts of the AC-type plasma display panel structure which is a first conventional art.
A pair of glass substrates (a front substrate 101 and a rear substrate 102) facing to each other is installed in the AC-type plasma display panel. Transparent sustaining electrodes 103, transparent odd-numbered scanning electrodes 104a, and transparent even-numbered scanning electrodes 104b are installed at the side, facing the rear substrate 102, of the front substrate 101. The sustaining electrodes 103, odd-numbered scanning electrodes 104a, and even-numbered scanning electrodes 104b are extended in the horizontal direction of the panel. Trace electrodes 106 are positioned to overlap with the sustaining electrode 103, odd-numbered scanning electrode 104a, and even-numbered scanning electrode 104b, respectively. The trace electrode 106 is made of a metal, for example, and is provided in order to reduce the electrode resistance value between each electrode and the external driving device. Also installed is a dielectric layer 112 covering the sustaining electrodes 103, odd-numbered scanning electrodes 104a, and even-numbered scanning electrodes 104b. A protective layer 114 composed of magnesium oxide protecting the dielectric layer 112 from being discharged is further provided.
At the side, facing the front substrate 101, of the rear substrate 102, data electrodes 107 which intersect at right angle with the sustaining electrodes 103 and scanning electrodes 104a and 104b are installed. Accordingly, the data electrodes 107 are extended in the vertical direction of the panel. Also installed on the data electrodes 107 is a dielectric layer 113 covering the data electrodes 107. Further, partition walls 109 separating the display cell in the horizontal direction are installed on the dielectric layer 113. Still further, fluorescent layers 111 converting the ultraviolet light, which is emitted by discharging of gases, into the visible light are formed on the side surfaces of the partition walls 109 and on the surface of the dielectric layer 113. Spaces for discharge gases 108 are secured between the front substrate 101 and rear substrate 102 with the partition walls 109. The discharge gas such as helium, neon, xenon, etc. or their mixture is filled into the spaces 108.
The display lines are formed between a scanning electrode and a sustaining electrode in the plasma display panel. In the meantime, all sustaining electrodes are shorted and called the common electrodes as the same waveform is applied to all sustaining electrodes. Such structure is referred to as an SC structure hereinafter.
Next, the memory-run-type driving operation in the plasma display panel having the above-described SC structure is described below.
FIG. 2 is a timing chart of sequence showing the writing-selective-type driving operation of the conventional plasma display panel. In this sequence one sub-field is composed of four periods including a priming period, addressing period, sustaining period, and sustainment-erasing period which are set sequentially.
First, in the priming period, the sawtooth-wave priming pulse Ppr-s is applied to the scanning electrodes and the rectangular-wave priming pulse Ppr-c is applied to the sustaining electrodes. The sustaining pulse voltage Vs is the reference potential of all pulses in this specification. The voltage pulse which is lower than the sustaining pulse voltage Vs is referred to as the negative polarity pulse, and the voltage pulse which is higher than the sustaining pulse voltage Vs is referred to as the positive polarity pulse.
The priming discharge occurs between the scanning electrode and sustaining electrode as the priming pulses Ppr-s and Ppr-c are applied thereto. As a result, active particles that facilitate the sustaining discharge of the cells thereafter are produced, wall charges with negative polarity is generated on the scanning electrodes, and wall charges with positive polarity is generated on the sustaining electrodes. Subsequently, the charge adjustment pulse Ppe-s is applied to the scanning electrodes. As a result, weak discharging occurs, and the negative polarity wall charges on the scanning electrodes and the positive polarity wall charges on the sustaining electrodes are reduced.
The next addressing period is the selection period of display cells that emit the light. During the addressing period, Pbw-s as the reference voltage is applied to the scanning electrodes and the scanning pulse Puw-s is applied to in the scanning sequence. Also, the data pulses Pd are applied to the data electrodes according to an image data.
The data pulse Pd is a pulse for selecting display cells. If the scanning pulse Puw-s and data pulse Pd are synchronized with each other, the writing discharge occurs at the intersection of the corresponding scanning electrode and data electrode. In the display cell with the writing discharge occurred, wall charges with positive polarity are generated on the scanning electrode, and wall charges with negative polarity are generated on the sustaining electrode. Whereas, in the display cell without the writing discharge occurred, the charging arrangement state when the charge adjustment pulse Ppe-s is applied to in the priming period is maintained.
The sustaining period after the addressing period is a period for display luminescence. During the sustaining period, application of the sustaining pulses from the sustaining electrodes side are initiated, after which the sustaining pulses Psus-s and Psus-c with negative polarity are applied to the scanning electrodes and sustaining electrodes with the sustaining pulse voltage Vs alternately. At this time, no sustaining discharge occurs even when the sustaining pulses are applied to the display cell, because the amount of wall charges of the display cell where writing is not performed during the addressing period is extremely small. In the meantime, in the display cell with the writing discharge occurred during the addressing period, the sustaining pulse voltage with negative polarity to the sustaining electrodes and wall charge voltage are superposed, and discharging occurs as the voltage between the electrodes exceeds the initial discharging voltage since the positive wall charges are remained on the scanning electrode and the negative wall charges are remained on the sustaining electrode. The sustaining pulse which is applied to initially is set to have a greater pulse width compared to that of the sustaining pulses that are continued thereafter so as to ensure sustaining discharge of the display cell which is selected during the addressing period as disclosed in Japanese Patent No. 2,674,485.
Once discharge occurs, the wall charges are positioned to counteract the voltage that is applied to each electrode. Therefore, the negative charges are generated on the sustaining electrode, while the positive charges are generated on the scanning electrode. Since the next scanning pulse becomes the positive-voltage pulse at the scanning electrode side, the effective voltage that is applied to the discharging space by superposing it with the wall charges exceeds the initial discharging voltage thus generating discharge. Therefore, in the same way, discharge is maintained as the periods that are shown to be “a” and “b” in FIG. 2 are repeated. Brightness of each sub-field is determined according to the frequency of repetition of discharging.
Finally, during the sustainment-erasing period, the sustaining erasing pulses Pse-s with negative polarity are applied to the scanning electrodes. The negative polarity sustaining erasing pulses Pse-s are the sawtooth-wave pulse. Then, the wall charges that are generated on each electrode in case that the sustaining discharge is being executed are cancelled and discharging is stopped.
In actual driving, the gradation display is achieved as a multiple number of sub-fields having different luminous intensities are combined to form one field by varying the number of sustaining pulses when the time from the priming period to the sustainment-erasing period is set to be one sub-field as shown here.
FIG. 3 is a perspective diagram of relevant parts of the AC-type plasma display panel structure which is a second conventional art. The same reference numerals are given to the compositional elements of the second conventional art shown in FIG. 3 as those given to the first conventional art shown in FIG. 1, and their duplicate illustration is omitted.
In the plasma display panel of the SC structure shown in FIG. 1, there are always at least two trace electrodes in the display cell. These trace electrodes lower brightness as they cut off the display light. A structure in which one sustaining electrode is shared by two vertically connected cells in order to reduce the number of trace electrodes is disclosed in Japanese Patent Laid-Open Publication No. Hei. 2-226639. Hereinafter, a structure in which one sustaining electrode is shared is referred to as an SCS structure in this specification.
In the second conventional art, the SCS structure is adopted. FIG. 4 is a schematic diagram showing the layout of electrodes in the SCS structure.
As shown in FIG. 4, the SCS structure is basically the same as the SC structure except that the sustaining electrode is shared by the upper display cell and lower display cell. However, it is possible to obtain a high brightness since the area occupied by the trace electrodes that cut off the display light is ¾ of the SC structure.
FIGS. 5A and 5B are schematic diagrams showing that only one line is emitted between the odd-numbered scanning electrode and sustaining electrode in the conventional driving sequence in the plasma display panel of the SCS structure. FIG. 5A shows the mode of emission during the period a in FIG. 2, i.e., during the period when the sustaining electrode is positive, and FIG. 5B shows the mode of emission during the period b in FIG. 2, i.e., during the period when the sustaining electrode is negative. As shown in FIGS. 5A and 5B, the range of emission when the sustaining electrode is negative is different from that when the sustaining electrode is positive. That is, emission of the light is expanded beyond the trace electrode of the sustaining electrode when the sustaining electrode is negative, but emission of the light is not expanded beyond the trace electrode of the scanning electrode when the sustaining electrode is positive, provided that it looks as if emission of the light were expanded to the sustaining electrode side a little since emission of the light of both polarities is added up and viewed actually.
The reason for wide expansion of emission of the light at the negative polar side is the property of discharging that emission of the light is stronger near the negative electrode in the negative glow region since the ultraviolet light by discharging of the negative glow occurred in the negative electrode is used mainly in the plasma display panel.
In the meantime, the cells emitted in the odd-numbered field is different from those emitted in the even-numbered field if the plasma display panel is run in the interlace mode. That is, only the display cells including the odd-numbered scanning electrode are emitted in the odd-numbered field, and only the display cells including the even-numbered scanning electrode are emitted in the even-numbered field.
FIG. 6 is a schematic diagram showing the mode of emission of each display cell in the interlace mode. The cells with hatching are the cells that can emit light in FIG. 6.
FIG. 7 shows the case where the plasma display panel of the SCS structure shown in FIG. 3 is operated in accordance with the waveform shown in FIG. 2 in the progressive mode. That is, the sustaining discharge is performed between the odd-numbered scanning electrode and sustaining electrode and between the even-numbered scanning electrode and sustaining electrode in the same field.
FIGS. 8A and 8B are schematic diagrams showing the mode of emission when the progressive mode is adopted in the plasma display panel of the SCS structure. FIG. 8A shows the mode of emission during the period a in FIG. 2, i.e., during the period when the sustaining electrode is positive, while FIG. 8B shows the mode of emission during the period b in FIG. 2, i.e., during the period when the sustaining electrode is negative. The sustaining electrode is negative and the sustaining pulse is applied to in the period b in FIG. 2. As shown in FIG. 8B, the range of emission between the odd-numbered scanning electrode and sustaining electrode is superposed with that between the sustaining electrode and even-numbered scanning electrode at the upper and lower portions of the sustaining electrode.
As described above, emission of the light by the sustaining discharge is expanded to neighboring cells on the shared electrode if the plasma display panel of the SCS structure is run in the conventional method. For this reason, emission of the light at the boundary of display lines sharing the sustaining electrode becomes stronger, and it looks as if the display lines existed continuously at an interval of two lines. This lowers the vertical resolution, making the quality of images undesirable.
If the display cells including the odd-numbered scanning electrode emit the light, the mode of emission of the light of each display cell is the same as that shown in FIGS. 5A and 5B, for example, and emission of the light is expanded to neighboring cells while the sustaining electrode becomes negative. Also, in the even-numbered field, emission of the light is expanded to neighboring cells on the sustaining electrode. In the interlace mode, emission of the light of the cells that are next to each other up and down is separated in view of the time, but actually, emission of the light of the odd-numbered field and even-numbered field is added and viewed. For this reason, the vertical resolution is lowered as in the progressive mode.
Also, in the progressive mode, if any one side of the sustaining electrode is selected, emission of the light is expanded to neighboring cells, but if both sides of the sustaining electrode are selected, emission of the light is offset that much. For that reason, brightness per cell of the corresponding cell is changed according to the state of selection of neighboring cells. Further, the above problem occurs simultaneously if the interlace method is mixed with the progressive method. Still further, brightness per area on an average is lowered in the same discharging frequency since the number of display cells that emit the light in the same time in the interlace method is ½ of that in the progressive method irrespective of the panel structure.